Heretofore, in a manufacturing process of a semiconductor device, plasma processing techniques have been used to perform film-forming and etching for a semiconductor wafer.
FIG. 1 is a sectional view of a reactive ion etching (RIE) apparatus which comprises a reaction chamber 2 for subjecting a semiconductor wafer 1 to etching, and a showerhead type upper electrode 3 and a lower electrode 4 arranged, respectively, on upper and lower sides of the reaction chamber 2 in opposed relation to each other.
As a principle, when an etching gas is supplied into the reaction chamber 2, and electric power is applied from a high-frequency power supply 10 to the lower electrode 4, plasma is generated in the reaction chamber 2. In the case where the RIE apparatus is a parallel plate-type RIE apparatus as depicted in FIG. 1, upon application of electric power from the high-frequency power supply 10 to the lower electrode 4, a self-bias potential is generated between the semiconductor wafer 1 and the plasma, and active species such as ions and radicals in the plasma are accelerated in a direction toward the semiconductor wafer 1 (direction perpendicular to a wafer surface). The active species can etch (anisotropically etch) the semiconductor wafer 1 only in the direction perpendicular to the wafer surface, based on a physical effect and a chemical reaction effect of sputtering, thereby enabling high-accuracy microprocessing.
In operation of etching the semiconductor wafer 1, an internal space of the reaction chamber 2 is first evacuated to a vacuum state by a vacuum pump (not depicted) connected to an downstream side of an exhaust plate 7, and the etching gas is supplied from the shower head type upper electrode 3.
The showerhead type upper electrode 3 is composed of a disk-shaped member having a hollow portion 5, and comprising a lower wall formed with a large number of gas supply holes 6 in a showerhead-like arrangement. The etching gas is supplied from an etching gas supply source (not depicted) to the hollow portion 5 and then supplied into the reaction chamber 2 through the gas supply holes 6 in a uniform flow rate distribution.
After the supply of the etching gas, electric power is applied from the high-frequency power supply 10 to the lower electrode 4, so that plasma is generated in the reaction chamber 2. The semiconductor wafer 1 is etched by active species in the plasma.
The semiconductor wafer 1 is electrostatically-attracted and held by a disc-shaped electrostatic chuck 8 (ESC) provided on an upper side of the lower electrode 4, and an annular edge ring 9 is provided around an upper surface of the electrostatic chuck 8. The edge ring 9 is provided as a means to adjust an electric field to prevent the active species from being deflected by an outer periphery of the semiconductor wafer 1 with respect to a vertical direction (the direction perpendicular to the wafer surface) during the etching of the semiconductor wafer 1.
Patent Document 1 (JP 2007-112641 A) describes a technique intended to provide a focus ring (edge ring) having plasma resistance to high-density plasma, wherein the focus ring is formed of a sintered composite obtained by: adding an organic binder to an mixed powder of yttria powder and aluminum powder; kneading and forming the resulting mixture to prepare a shaped body; and then burning the shaped body in a hydrogen or inert atmosphere at a temperature of 1520° C. or less, wherein the focus ring has a specific resistance (electric resistivity) of less than 109 Ω·cm.
Patent Document 2 (JP H11-217268A) describes a SiC sintered body for a plasma apparatus, which exhibits excellent plasma resistance and has a low risk of particle contamination due to drop-off of particles, wherein the SiC sintered body has a density of 2.7 g/cm3 or more, an average crystal grain size of 20 μm or more, a thermal conductivity of 80 W/m·K or more, and an electric resistivity of 10−2 to 102 Ω·cm. Although the Patent Document 2 discloses sintered bodies using α-SiC as a primary raw material, in Examples 3 and 5, it also discloses sintered bodies using β-SiC as a primary raw material in detail in Examples 1, 2 and Comparative Examples 1, 2 with detailed description. As regards the sintered bodies using α-SiC as a primary raw material, properties thereof are not shown, except for the matters described in Table 1. Specifically, as to a content rate of free carbon, Table 1 presents higher values than those of the remaining Examples and Comparative Examples, and, as to electric resistivity, presents relatively high values, specifically, 0.4 Ω·cm in Example 3 and 5.0 Ω·cm in Example 5. Thus, the sintered bodies in Examples 3 and 5 are not formed to have particularly excellent properties.
Moreover, although the sintered body in Example 3 is sintered at a highest temperature of 2400° C., the density thereof is 3.1 g/cm3 at most, and the crystal grain size is less than those of Examples 1 and 2. Thus this sintered body is more likely to be charged with electric charges, and is thus inferior in plasma resistance.
Patent Document 3 (JP 2003-095744A) includes the following descriptions in paragraph [0008]: “as shown in Sample No. 2 to Sample No. 13, the silicon carbide sintered body of the present invention is understand to be a sintering material which is excellent in strength and hardness based on a dense and substantially pore-free microstructure over which a YAG phase is finely dispersed.” (lines 31 to 34 of 5th column); and “When a semiconductor-producing member using the silicon carbide sintered body of the present invention in each of Sample Nos. 2 to 13 and Sample Nos. 16 and 17 was mounted on a semiconductor-manufacturing device, diffuse reflection due to pores was remarkably suppressed, so that device accuracy was improved and improvement in semiconductor manufacturing efficiency was ascertained.” (lines 35 to 39 of 6th column). However, as described in the paragraph [0008] as follows: “crystal regions of silicon carbide exhibited substantially the same physical property values, irrespective of which of α phase, β phase and α+β composite phase each of the crystal regions has” (lines 36 to 38 of 5th column), Patent Document 3 makes no mention of recognition that the sintered body made of the α-phase silicon carbide crystal phase is particularly excellent.
Further, recently, an edge ring formed of silicon carbide (hereinafter referred to as “SiC”) having high plasma resistance has become widespread. In this regard, with a view to preventing metal contamination in the reaction chamber 2, high-purity SiC prepared by a chemical vapor deposition (CVD) process, or a sintered body obtained by hot-pressing a SiC powder prepared by a CVD process, is employed, and a primary raw material thereof is β-structure silicon carbide (hereinafter referred to as “β-SiC”).
The SiC member using α-silicon carbide (hereinafter referred to as “α-SiC”) as a primary raw material has been considered to cause chamber contamination, because it contains metal impurities such as iron in an amount greater than those in the SiC member prepared by CVD process using β-SiC as a primary raw material. For this reason, an idea of using α-SiC as a raw material for a member for a plasma processing apparatus has been unlikely to be created, and plasma resistance of α-SiC has not been checked in detail.